Keywords: soil compaction, soil suction, stiffness, unsaturated soil, pore pressure development

Transcription

1 Prediction of compction curve Nure Kurucuk Fcult of Engineering, Monh Univerit, Clton, VIC, Autrli Jnth Kodikr Fcult of Engineering, Monh Univerit, Clton, VIC, Autrli Delwn Fredlund Golder Aocite, Sktoon, Sktchewn, Cnd. Keword: oil compction, oil uction, tiffne, unturted oil, pore preure development ABSTRACT Compction of oil i one of the mjor ctivitie in geotechnicl engineering involving erthwork. Compction curve generll feture n inverted prbolic hpe nd i ued to find the optimum wter content tht mximie dr denit. Since it introduction b Proctor in 933, everl reercher hve provided qulittive explntion for the generl hpe of the compction curve. Furthermore, there i vt bod of literture covering the behviour of compcted oil. However, fundmentl reerch on the compction proce nd the evolution of compction chrcteritic re limited. Therefore, in order to undertnd the driving mechnim of compction, thi pper invetigte the effect of oil uction nd tiffne in the hpe of the compction curve, from unturted oil mechnic tndpoint. On the bi of unturted oil mechnic principle, theoreticl prediction of the prbolic hpe of the compction curve i provided. INTRODUCTION Soil compction i widel ued in geo-engineering nd i importnt for the contruction of rod, dm, lndfill, irfield, foundtion, hdrulic brrier, nd ground improvement. Compction i pplied to the oil, with the purpoe of finding optimum wter content to mximie it dr denit, nd therefore, to decree oil compreibilit, incree it hering trength, nd in ome ce, to reduce it permebilit. Proper compction of mteril enure the durbilit nd tbilit of erthen contruction. A tpicl compction curve preent different denifiction tge when the oil i compcted with the me pprent energ input but different wter content. The wter content t the pek of the curve i clled optimum wter content (OWC) nd repreent the wter content in which dr denit i mximized for given compction energ. Since Proctor` pioneering work in 933, mn reercher hve ttempted to explin the leding mechnim in the denifiction tge, minl on the dr ide of optimum wter content. The compction curve w explined in term of cpillrit nd lubriction (Proctor, 933), vicou wter (Hogentogler, 936), pore preure theor in unturted oil (Hilf, 956), phico-chemicl interction (Lmbe, 960), nd concept of effective tre theor (Olon, 963). Moreover, Brden nd Side (970) undertook n experimentl reerch on the reltion between the engineering performnce of compcted unturted cl nd microcopic obervtion of cl tructure. In ddition, Lee nd Suedkmp (97) conducted reerch on the hpe of the compction curve for different oil. Thee work provide predominntl qulittive explntion of the hpe of the curve. Depite thi reerch work, nd the importnce nd high demnd of the compction proce in engineering prctie, it till remin tht the compction of oil i quite complex nd not well explined, prticulrl from quntittive ene. Therefore, there i need for reerch to be undertken t fundmentl level to undertnd the evolution of compction chrcteritic of oil nd the inverted prbolic hpe of the compction curve. Thi pper preent theoreticl prediction of the compction curve for nd uing unturted oil mechnic principle. In order to chieve thi im, pproche developed b Hilf (948) nd Fredlund & Rhrdjo (993) for undrined loding proce re imulted. Volume chnge of compcted oil re clculted uing the volume chnge theor from unturted oil mechnic, nd re ued o predict theoreticl compction curve.

2 MODELLING OF COMPACTION CURVES. Theoreticl bckground Theoreticl concept utilized for the development of oil compction curve re preented in thi ection. Initill, Hilf (948) nd Fredlund & Rhrdjo (993) pproche for pore preure development re preented. Thi i continued with Fredlund & Morgentern (976) volume chnge theor for compcted oil nd the derivtion of the dr denit of oil... Pore preure development during ttic compction One of the min imultion for the genertion of the compction curve i tht of pore preure development. Hilf (948) developed reltionhip between pore preure nd pplied tre, which i bed on one-dimenionl oil compreion, Bole lw, nd Henr lw, nd i expreed follow: Δ u Δσ ( S0 + hs0) n 0 + ( u0 +Δu) m v () where; Δ u chnge in bolute pore ir preure, S 0 initil degree of turtion, h coefficient of olubilit, n 0 initil poroit, u 0 initil bolute ir preure, m v coefficient of volume chnge in turted oil, nd Δ σ chnge in pplied verticl tre. Hilf (948) developed thi eqution uming tht ir nd wter phe re undrined, nd volume reduction i due to ir diolving in the wter nd compreion of free ir. Both liquid nd olid prt were conidered to be incompreible. He lo umed tht the chnge in ir preure i equl to the chnge in pore wter preure, nd therefore, mtric uction chnge w inignificnt. Thee umption will be reviewed further in Section.. On the other hnd, Fredlund & Rhrdjo (993) developed n eqution for undrined loding for pore preure chnge b uing pore preure prmeter: Δ u BΔ σ () Δ uw BwΔ σ (3) where; pplied verticl tre. B pore ir preure prmeter, B pore wter preure prmeter, nd w Δ σ chnge in Thi pproch ume tht oil prticle re incompreible, but the fluid phe re compreible. In contrt to the pproch b Hilf (948), mtric uction chnge were tken into ccount. It w ccepted tht ir nd wter preure become equl t turtion. Therefore, mtric uction will decree from the initil vlue to zero t turtion. Pore ir ( B ) nd pore wter ( B w) preure prmeter re defined follow: RR3 R4 B R R 3 (4); R RR 4 Bw. (5) R R 3 In Eqution 4 nd 5, R, R, R nd 3 R re defined : 4 ( ) ( ) m / m S+ hs n/ u m R m / m + SnC / m w (6); R m / m + SnC / m w (7) R 3 m / m m m S hs n u m / + / ( ) ( ) (8); R4 m / m S + hs n/ u m ( ) ( ) (9)

3 where; m compreibilit of oil prticle with repect to net tre ( σ u), m compreibilit of oil prticle referenced to uction ( u, m compreibilit of ir phe with repect to net tre ( σ u ), m compreibilit of ir phe with repect to uction ( u, u bolute pore ir preure S degree of turtion, h coefficient of olubilit, n poroit, nd C compreibilit of wter. w.. Computtion of volume chnge nd dr denit The volume chnge contitutive reltionhip propoed b Fredlund & Morgentern (976) for unturted oil i ued for the clcultion of compction curve, nd i expreed follow: ΔV V 0 v m Δ( σ u ) + m Δ( u u ) (0) w where; Δ V overll volume chnge of oil element, v V 0 initil totl volume of the oil element, m compreibilit of oil prticle with repect to net tre ( σ u), m compreibilit of oil prticle referenced to uction ( u, Δ( σ u ) chnge in net tre, nd Δ( u chnge in oil uction. Since oil prticle re incompreible, it i ccepted tht deformtion i primril due to compreion of the pore fluid (i.e., the ir nd wter mixture). The independent tre tte vrible concept i utilized in the derivtion; nmel, net tre ( σ u ) (cue reduction in volume with compreion), nd mtric uction tre ( u (generll reult in volume incree with compreion). Conequentl, overll volume chnge of the oil mple i clculted b multipling right hnd ide of Eqution 0 b the initil volume of the oil mple. Furthermore, the finl totl volume cn be obtined uing the volume chnge of the oil, nd thi give the correponding dr denit.. Etimtion of oil compction curve Figure : Pore ir preure development with pplied tre In order to produce compction curve for given et of prmeter, the pore ir preure development for Hilf` (948) nd Fredlund & Rhrdjo (993) pproche re plotted in Figure. The prmetric vlue ued in thi clcultion re given in thi figure. It hould be noted tht Fredlund & Rhrdjo` (993) pproch tke into conidertion the chnge in uction with

4 compreion, where Hilf (948) nli ume tht the uction chnge i negligible during compreion nd uction i equl to the initil mtric uction. Therefore, Hilf` (948) pproch produce lrger pore ir preure vlue thn Fredlund & Rhrdjo (993) pproch for given pplied tre. Uing the volume chnge eqution (Eqution 0) nd ir preure computed with pplied tre, (Figure ), compction curve re produced for both pproche hown in Figure. In Figure compreibilit coefficient re umed to be contnt nd their vlue re given on the figure. It hould be noted tht compction curve which i plotted uing Hilf (948) pproch doe not include the uction component of volume chnge theor (or umed m i umed equl to zero in Eqution 0). 00% turtion Figure : Compction curve for contnt coefficient of compreibilit It i cler tht thi method (uing contnt compreibilit coefficient (m v, m, m, in fct it cn be hown tht m v m ) cn produce reonble hpe for the compction curve on the wet ide of OWC, but not on the dr ide of OWC. Moreover, uction chnge tht i included in Fredlund & Rhrdjo (993) pproch reult in ome reduction in dr denit, but doe not chnge the hpe of the compction curve t lower wter content. In order to exmine the likel uction chnge during compction, conidertion i given to the experimentl reult produced b Montnez (00), hown in Figure 3. Montnez (00) produced uction contour for compcted nd-bentonite mixture ocited with domin defined b compction curve t vriou pprent energ level. He found tht mtric uction onl decree mrginll with denit incree nd in mn ce cn be conidered contnt. Therefore, Hilf nli of uming contnt uction during compction pper to be cloe to the rel itution, but direct dt meured during compction proce m be ueful to vlidte thi umption Compction energ Hev Stndrd Dr denit ( Mg/m ) kp 498 kp 780 kp 374 kp 8 kp 84 kp Sr 00%.50 Contour of equl uction Wter content (%) Figure 3: Dt for uniform nd-bentonite (0%) mixture (dopted from Montnez, 00)

5 Furthermore, even if there i mll uction decree with compction, m pplicble to the unloding proce cn be conidered mller thn tht pplicble to loding proce. Therefore, the effect of the uction component ( in the econd component of Eqution 0) cn be conidered not ver ignificnt. With thi inight, the focu on the compction proce fll on the coefficient of oil compreibilit due to net tre, m. In the following prt of the pper, the influence of coefficient of compreibilit due to net tre (m ) on the hpe of the compction curve i preented. Direct dt relted to the vrition of m with turtion re not vilble. However, ome inight cn be gined from the her-wve velocit meured b Cho nd Sntmrin (00) in grnite powder t vriou turtion, hown in Figure 4, to explin the reltionhip between m nd degree of turtion. Figure 4: Sher-wve velocit dt for grnite powder (dopted from Cho & Sntmrin, 00) It i cler from Figure 4 tht the her-wve velocit (v ), hence her modulu (v G/ρ ) of the oil incree with decreing turtion (or converel oil compreibilit decree). Therefore, it cn be rgued tht m will decree with decreing turtion in ome form. On thi bi, reltionhip between m nd degree of turtion i plotted hown in Figure 5. Figure 5: Chnge in m vlue with initil degree of turtion

6 When the vrition of m with degree of turtion i tken into ccount, the reulting compction curve re hown in Figure 6. Clerl, now the proper hpe of the compction curve cn be produced. Moreover, it i cler tht the dependenc of compction curve t different tre level (or energ input) i reonbl well cptured, where optimum wter content hift to the right with higher tre level. 3 CONCLUSIONS Figure 6: Compction curve for different energ level Thi pper preent the theoreticl concept relted to the prediction of the compction curve. For the firt time, it highlight the fct tht hpe of the compction curve cn be predicted uing unturted oil mechnic principle. The min inight gined w tht the chnge in mtric uction i not importnt for the evolution of the compction tte, but the influence of mtric uction on the mteril compreibilit with repect to net tre i the governing fctor determining the compction denit. Therefore, it cn be reoned tht the inverted prbolic hpe of the compction curve i direct function of the vrition of the mteril compreibilit with degree of turtion. More reerch, however, i necer to reinforce thee concept. REFERENCES Brden, L., nd Side, G. R. (970), Engineering behviour nd tructure of compcted cl, Journl Soil Mechnic nd Foundtion Diviion, ASCE, 96, No. SM4, 7. Cho, G. C., nd Sntmrin, J. C. (00), Unturted prticulted mteril Prticle level tudie, Journl of Geotechnicl nd Geoenvironmentl Engineering, 7(), Fredlund, D. G., nd Morgentern, N. R. (976), Contitutive reltion for volume chnge in unturted oil, Cndin Geotechnicl Journl, 4, 3, Fredlund, D. G., nd Rhrdjo, H. (993), Soil mechnic for unturted oil, p. 9-94, John Wile & Son. Hilf, J. W. (956), An Invetigtion of Pore Wter Preure in Compcted Coheive Soil, Technicl Memorndum 654, U. S. Deprtment of the Interior, Bureu of Reclmtion, Denver, Colordo. Hogentogler, C. A. (936), Eentil of oil compction, Proceeding Highw Reerch Bord, Ntionl Reerch Council, Whington, D.C., Lmbe, T. W. (960), Structure of compcted cl, Trnction, ASCE, 5, Lee, D. Y., nd Suedkmp, R. J. (97), Chrcteritic of irregulrl hped compction curve of oil, Highw Reerch Bord, 38, -9. Montnez, J. E. C. (00), Suction nd volume chnge of compcted nd-bentonite mixture, PhD thei, Univerit of London, Imperil College of Science, London, Englnd. Olon, R. E. (963), Effective tre theor of oil compction, Journl Soil Mechnic nd Foundtion Diviion, ASCE, 89, No. SM, Proctor, R. R. (933), Fundmentl Principle of Soil Compction, Engineering New-Record,, 86.